(1) Field of the Invention
This invention is broadly concerned with the field of the technique of stabilizing an air-fuel ratio in the high load, high speed range of an air valve type carburetor of an engine for vehicles such as a car.
(2) Description of the Prior Art
As is well known in the art, a variety of carburetors are available for engines of cars or the like and they have both merits and demerits. Among them, a so-called air valve type carburetor has gained a wide application because it provides excellent high load, high speed performance.
The air valve type carburetor will be now outlined with reference to FIG. 1. A barrel 1 is interconnected to an engine, not shown, via an intake manifold. When a throttle valve 2 of this barrel 1 is fully open in the interlocking arrangement with a throttle valve on the primary side, not shown, and the engine operation changes to the high speed, high load operation, an air valve 4 of an air horn 3 gradually opens to a balanced state in accordance with an intake air quantity against the force of a return spring 5 so that a metering needle 7, which is pivotally supported by a pin at the tip of a link 6 interconnected to the air valve 4, is loosely raised inside a through-hole 8 of the air horn 3, expanding metering opening with respect to a jet 10 that is disposed in a float chamber 9. The fuel 11 thus metered is applied to a well 12 and is mixed and emulsified with bleed air by an emulsion pipe 14 connected to an air bleed 13. The mixture is discharged as a rich air-fuel mixture from a main nozzle 15 that is disposed between the throttle valve 2 and the air valve 4.
An air connector 16, which is disposed on the air horn 3 as shown in the drawing, is connected, via a duct 17, to an air cleaner 18 disposed at a predetermined position inside an engine room. According to this arrangement, the air sucked into the air connecter 16 is applied from the air valve 4 to the barrel 1 and is also communicated with the float chamber 9 via the through-hole 8 of the metering needle 7.
Accordingly, the intake air pressure changes with the reciprocating revolution of the engine. Intake pulsation occurs especially strongly inside the carburetor, disposed separately from the air cleaner, during the high load, high speed operation of the engine.
Intake pulsation also affects the float chamber also from the through-hole 8 as shown in FIG. 1 in such a manner as to push down the surface of the fuel oil immediately below the through-hole 8 in the conelike form. If this phenomenon proceeds, the jet 10 sucks the air and the air-fuel mixture becomes excessively lean, deteriorating engine drivability. In such a case, the excellent high load, high speed performance inherent to the air valve type carburetor can no longer be obtained.